This invention relates to a damper adapted for use in a vehicle suspension system, and more particularly to a hydraulic damper utilizing a Magneto-Rheological fluid.
Dampers, such as shock absorbers and MacPherson struts have been used for many years in vehicle suspension systems for dissipating energy and reducing undesirable road inputs that would otherwise be transferred to the vehicle body and the associated passenger compartment. In recent years, hydraulic dampers using a special type of fluid, known as Magneto-Rheological (MR) fluid, have been utilized as part of vehicle traction and stability enhancement control systems, for actively controlling the amount of damping provided under varying road and operating conditions, to provide improved performance and safe operation of vehicles.
As shown in FIG. 1, in the past, one form of Magneto-Rheological (MR) dampers 10 has typically included a piston 12 that is movable within a working chamber 14 of a cylinder 16 containing the MR fluid. The cylinder 16 is attached to one part of the suspension, and a piston rod 18 extending from the piston 12 and out of the cylinderl6 is attached to another part of the vehicle suspension.
The piston 12 of the MR damper 10 separates the working chamber 14 into a compression chamber 20 and a rebound chamber 22. The piston 12 is equipped with a sliding fluid seal 24 that prevents leakage of the fluid around the piston 12, between the piston 12 and the cylinder 16. The piston 12 also includes one or more smooth-walled flow passages 26 extending though the piston 12 that allow the MR fluid in the working chamber 14 to move between the compression and rebound chambers 20,22, as the piston rod 18 and piston 12 are moved in relation to the cylinder 16 of the damper 10 by movement of the vehicle suspension. The flow passages 26 extending through the piston 12 are sized to restrict the flow of MR fluid through the piston 12, thereby limiting the rate at which the piston 12 can move within the cylinder 16 to be a function of how rapidly the MR fluid can pass through the flow passages 26.
The MR fluid has microscopic particles of a magnetic material suspended in a liquid carrier. When the MR fluid is exposed to a magnetic field of sufficient strength, the suspended particles align with the magnetic field and cause a change in the viscosity of the MR fluid. As the viscosity of the MR fluid changes, the rate at which the MR fluid can flow through the flow passages 26 in the piston 12 is also changed, thereby causing the amount of damping to be changed in a direct relationship to the viscosity of the MR fluid flowing through the flow passages 26.
In one form of MR damper 10, the piston 12 includes an electromagnetic coil 28 oriented within the piston 12 to generate an electromagnetic field acting across one or more of the flow passages 26 in the piston 12. By controlling the electrical current to the electromagnetic coil 28, the viscosity of the MR fluid within the flow passages 26 can be changed to adjust the amount of damping provided to meet the operational requirements of the damper 10 for various vehicle operating conditions, resulting in continuously variable real time damping. U.S. Pat. No. 5,277,281 to Carlson, et at, discloses a number of specific embodiments of MR dampers of the type described above.
The change in viscosity of the MR fluid that can be attained in an MR damper 10 of the type described above, and the resulting change in damping provided by the damper 10, are directly related to the intensity of the magnetic flux within the flow passages 26 of the piston 12. It is therefore desirable that the MR damper 10 be designed to provide efficient and effective conversion of the electrical current applied to the electromagnetic coil 28 to produce an optimal strength magnetic field.
My invention provides an improved MR damper through the use of a piston having judiciously placed grooves in the walls of a magnetic flux path portion of a fluid flow passage through the piston. The grooves result in a focusing and intensification of the magnetic flux emanating from corners of the grooves, to thereby intensify the magnetic flux impressed across the fluid flow passage and cause a greater degree of change in viscosity of the MR fluid flowing through the passage than is achievable in prior MR dampers having smooth-walled fluid flow passages.
In one form of my invention a vehicle damper includes a cylinder tube and a reciprocating piston slidably disposed in the working chamber. The cylinder tube defines an axis and a working chamber extending along the axis for containing a magneto-rheological (MR) fluid therein. The piston includes a first and a second face and a fluid passage extending through the piston from the first to the second face for directing a flow of MR fluid along a flow direction through the flow passage as the piston reciprocates in the working chamber. The piston has an electromagnetic element defining a wall forming a magnetic flux path portion of the fluid flow passage. The wall includes a groove therein extending in a direction generally transverse to the flow direction through the magnetic flux path portion of the fluid flow passage, to thereby intensify a magnetic flux passing through the magnetic flux path portion of the fluid flow passage.
The foregoing and other features and advantages of my invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, with the scope of the invention being defined by the appended claims and equivalents thereof.